Diffuser pipe exit flare

ABSTRACT

A diffuser pipe has a tubular body defining a pipe center axis extending therethrough. The tubular body includes a first portion extending in a generally radial direction from an inlet of the tubular body, a second portion extending in a generally axial direction and terminating at a pipe outlet, and a bend portion fluidly linking the first portion and the second portion. The tubular body has a length defined between the inlet and the pipe outlet. The tubular body has cross-sectional profiles defined in a plane normal to the pipe center axis. An area of the cross-sectional profile at the pipe outlet is at least 20% greater than an area of the cross-sectional profile at a point upstream from the pipe outlet a distance corresponding to 10% of the length of the tubular body.

TECHNICAL FIELD

The present application relates generally to centrifugal compressors forgas turbine engines, and more particularly to diffuser pipes for suchcentrifugal compressors.

BACKGROUND

Diffuser pipes are provided in certain gas turbine engines for diffusinga flow of high speed air received from an impeller of a centrifugalcompressor and directing the flow to a downstream component, such as anannular chamber containing the combustor. The diffuser pipes aretypically circumferentially arranged at a periphery of the impeller, andare designed to transform kinetic energy of the flow into pressureenergy. Diffuser pipes seek to provide a uniform exit flow with minimaldistortion, as it is preferable for flame stability, low combustor loss,reduced hot spots etc.

The diffuser pipes increase in cross-sectional area over their length,in order to provide diffusion of the air exiting the impeller. As thearea gradually increases, and the flow within the pipe reduces invelocity, separation of the flow begins to occur within the diffuserpipe. The effectiveness of the diffuser is related to its ability toraise the static pressure while limiting the total pressure loss due tothe diffusion.

SUMMARY

There is provided a compressor diffuser for a gas turbine engine, thecompressor diffuser comprising: diffuser pipes having a tubular bodydefining a pipe center axis extending therethrough, the tubular bodyincluding a first portion extending in a generally radial direction froman inlet of the tubular body, a second portion extending in a generallyaxial direction and terminating at a pipe outlet, and a bend portionfluidly linking the first portion and the second portion, the tubularbody having a length defined between the inlet and the pipe outlet, thetubular body having cross-sectional profiles defined in a plane normalto the pipe center axis, an area of the cross-sectional profile at thepipe outlet is at least 20% greater than an area of the cross-sectionalprofile at a point upstream from the pipe outlet a distancecorresponding to 10% of the length of the tubular body.

There is provided a diffuser pipe comprising a tubular body defining apipe center axis extending therethrough, the tubular body including afirst portion extending in a generally radial direction from an inlet ofthe tubular body, a second portion extending in a generally axialdirection and terminating at a pipe outlet, and a bend portion fluidlylinking the first portion and the second portion, the tubular bodyhaving a length defined between the inlet and the pipe outlet, thetubular body having cross-sectional profiles defined in a plane normalto the pipe center axis, an area of the cross-sectional profile at thepipe outlet is at least 20% greater than the area of the cross-sectionalprofile at a last 10% of the length of the tubular body.

There is provided a method of increasing a static pressure of fluidexiting a centrifugal compressor of a gas turbine engine, the methodincluding: conveying the fluid through a diffuser pipe to rapidlydiffuse the fluid through a last 10% of a length of the diffuser pipeover which a cross-sectional area of the diffuser pipe increases by atleast 20%.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a gas turbine engine;

FIG. 2 is a perspective view of an impeller and diffuser pipes of acentrifugal compressor of the gas turbine of FIG. 1;

FIG. 3 is a perspective view of one of the diffuser pipes of FIG. 2;

FIG. 4 is a graph plotting area at various locations along a length of adiffuser pipe, such as the one shown in FIG. 3;

FIG. 5 shows examples of flow stream lines through the diffuser pipe ofFIG. 3; and

FIG. 6 is a graph plotting equivalent cone angle (ECA) at variouslocations along a length of a diffuser pipe, such as the one shown inFIG. 3.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type preferably providedfor use in subsonic flight, generally comprising in serial flowcommunication along an engine center axis 11 a fan 12 through whichambient air is propelled, a compressor section 14 for pressurizing theair, a combustor 16 in which the compressed air is mixed with fuel andignited for generating an annular stream of hot combustion gases, and aturbine section 18 for extracting energy from the combustion gases. Thecompressor section 14 may include a plurality of stators 13 and rotors15 (only one stator 13 and rotor 15 being shown in FIG. 1), and it mayinclude a centrifugal compressor 19.

The centrifugal compressor 19 of the compressor section 14 includes animpeller 17 and a plurality of diffuser pipes 20, which are locateddownstream of the impeller 17 and circumferentially disposed about aperiphery of a radial outlet 17A of the impeller 17. The diffuser pipes20 convert high kinetic energy at the impeller 17 exit to staticpressure by slowing down fluid flow exiting the impeller. The diffuserpipes 20 may also redirect the air flow from a radial orientation to anaxial orientation (i.e. aligned with the engine axis 11). In most cases,the Mach number of the flow entering the diffuser pipe 20 may be at ornear sonic, while the Mach number exiting the diffuser pipe 20 may beless than 0.25 to enable stable air/fuel mixing, and light/re-light inthe combustor 16.

FIG. 2 shows the impeller 17 and the plurality of diffuser pipes 20,also referred to as “fishtail diffuser pipes”, of the centrifugalcompressor 19. Each of the diffuser pipes 20 includes a diverging (in adownstream direction) tubular body 22, formed, in one embodiment, ofsheet metal. The enclosed tubular body 22 defines a flow passage 29 (seeFIG. 3) extending through the diffuser pipe 20 through which thecompressed fluid flow is conveyed. The tubular body 22 includes a firstportion 24 extending generally tangentially from the periphery andradial outlet 17A of the impeller 17. An open end is provided at anupstream end of the tubular body 22 and forms an inlet 23 (see FIG. 3)of the diffuser pipe 20. The first portion 24 is inclined at an angle θ1relative to a radial axis R extending from the engine axis 11. The angleθ1 may be at least partially tangential, or even substantiallytangentially, and may further correspond to a direction of fluid flow atthe exit of the blades of the impeller 17, such as to facilitatetransition of the flow from the impeller 17 to the diffuser pipes 20.The first portion 24 of the tubular body 22 can alternatively extendmore substantially along the radial axis R.

The tubular body 22 of the diffuser pipes 20 also includes a secondportion 26, which is disposed generally axially and is connected to thefirst portion 24 by an out-of-plane curved or bend portion 28. An openend at the downstream end of the second portion 26 forms a pipe outlet25 (see FIG. 3) of the diffuser pipe 20. Preferably, but notnecessarily, the first portion 24 and the second portion 26 of thediffuser pipes 20 are integrally formed together and extendsubstantially uninterrupted between each other, via the curved, bendportion 28.

The large radial velocity component of the flow exiting the impeller 17,and therefore entering the first portion 24 of each of the diffuserpipes 20, may be removed by shaping the diffuser pipe 20 with the bendportion 28, such that the flow is redirected axially through the secondportion 26 before exiting via the pipe outlet 25 to the combustor 16. Itwill thus be appreciated that the flow exiting the impeller 17 entersthe inlet 23 and the upstream first portion 24 and flows along agenerally radial first direction. At the outlet of the first portion 24,the flow enters the bend portion 28 which functions to turn the flowfrom a substantially radial direction to a substantially axialdirection. The bend portion 28 may form a 90 degree bend. At the outletof the bend portion 28, the flow enters the downstream second portion 26and flows along a substantially axial second direction different fromthe generally radial first direction. By “generally radial”, it isunderstood that the flow may have axial, radial, and/or circumferentialvelocity components, but that the axial and circumferential velocitycomponents are much smaller in magnitude than the radial velocitycomponent. Similarly, by “generally axial”, it is understood that theflow may have axial, radial, and/or circumferential velocity components,but that the radial and circumferential velocity components are muchsmaller in magnitude than the axial velocity component.

Referring now to FIG. 3, the tubular body 22 of each diffuser pipe 20has a radially inner wall 22A and a radially outer wall 22B. The tubularbody 22 also has a first side wall 22C spaced circumferentially apartacross the flow passage 29 from a second side wall 22D. The radiallyinner and outer walls 22A, 22B and the first and second side walls 22C,22D meet and are connected to form the enclosed flow passage 29extending through the tubular body 22. The radially inner and outerwalls 22A, 22B and the first and second side walls 22C, 22D meet and areconnected to form a peripheral edge of the tubular body 22 whichcircumscribes the pipe outlet 25. The radially inner wall 22Acorresponds to the wall of the tubular body 22 that has the smallestturning radius at the bend portion 28, and the radially outer wall 22Bcorresponds to the wall of the tubular body 22 that has the largestturning radius at the bend portion 28.

The tubular body 22 diverges in the direction of fluid flow Ftherethrough, in that the internal flow passage 29 defined within thetubular body 22 increases in cross-sectional area between the inlet 23and the pipe outlet 25 of the tubular body 22. The increase incross-sectional area of the flow passage 29 through each diffuser pipe20 is gradual over some of diffuser pipe 20 and more abrupt in parts ofthe second portion 26, as described in greater detail below. Thedirection of fluid flow F is along a pipe center axis 21 of the tubularbody 22. The pipe center axis 21 extends through each of the first,second, and bend portions 24, 26, 28 and has the same orientation asthese portions. The pipe center axis 21 is thus curved. In the depictedembodiment, the pipe center axis 21 is equidistantly spaced from theradially inner and outer walls 22A, 22B of the tubular body 22, and fromthe first and second side walls 22C, 22D, through the tubular body 22.

Still referring to FIG. 3, the tubular body 22 has a length L definedfrom the inlet 23 to the pipe outlet 25. The length L of the tubularbody 22 may be measured as desired. For example, in FIG. 3, the length Lis the length of the pipe center axis 21 from the inlet 23 to the pipeoutlet 25. In an alternate embodiment, the length L is measured alongone of the walls 22A, 22B, 22C, 22D of the tubular body 22, from theinlet 23 to the pipe outlet 25. Reference is made herein to positions onthe tubular body 22 along its length L. For example, a position on thetubular body 22 that is along a last 10% of the length L is anywhere inthe segment of the tubular body 22 that is upstream of the pipe outlet25 a distance equal to 10% of the length L. This same segment is alsodownstream of the inlet 23 a distance equal to 90% of the length L.Similarly, a position on the tubular body 22 that is along a first 90%of the length L is anywhere in the segment of the tubular body 22 thatis downstream of the inlet 23 a distance equal to 90% of the length L.This same segment is also upstream of the pipe outlet 25 a distanceequal to 10% of the length L.

The tubular body 22 is composed of many cross-sectional profiles 27which are arranged or stacked one against another along the length L ofthe tubular body 22. Each cross-sectional profile 27 is a planar contourthat lies in its own plane that is transverse or normal to the pipecenter axis 21. FIG. 3 shows multiple cross-sectional profiles 27 inevery portion 24, 26, 28 of the tubular body 22, and it will beappreciated that many more cross-sectional profiles 27 may be defined atother locations along the pipe center axis 21. In the depictedembodiment, the orientation of the cross-sectional profiles 27 in theframe of reference of the diffuser pipe 20 may vary over the length L ofthe tubular body 22, depending on where the cross-sectional profiles 27are located along the pipe center axis 21. Each cross-sectional profile27 defines the shape, contour, or outline of the tubular body 22 at aspecific location along the pipe center axis 21.

Referring to FIG. 3, and as described in greater detail below, thecross-sectional profiles 27 vary over the length L of the tubular body22. The cross-sectional profiles 27 are different over the length L ofthe tubular body 22. Each cross-sectional profile 27 may be unique, andthus different from the other cross-sectional profiles 27. An area ofthe cross-sectional profiles 27 varies along the length L of the tubularbody 22. The area of a given cross-sectional profile 27 is definedbetween the inner, outer, first side, and second side walls 22A, 22B,22C, 22D in the cross-sectional profile 27. The area of thecross-sectional profiles 27 increases over the length L of the tubularbody 22 in the direction of the pipe outlet 25. This is consistent withthe diverging flow passage 29 defined by the tubular body 22.

FIG. 4 plots a normalized value for the area of the cross-sectionalprofiles 27 of the tubular body 22 at different points along the lengthL of the tubular body 22, where the length L is provided as a normalizedmeanline length. The “meanline” describes the locus of points from theinlet 23 to the pipe outlet 25 where each point is defined as the centerof each section. A final value for the cross-sectional area of thetubular body 22 is defined at the pipe outlet 25, and is shown in FIG. 4as corresponding to 100% of the normalized value for the area of thecross-sectional profile 27 at the pipe outlet 25. The final value is thehighest value for the cross-sectional area of the tubular body 22. FIG.4 shows the area curves for the tubular bodies 22 of diffuser pipes 20with different area distributions along their lengths L. Referring toFIGS. 3 and 4, the tubular body 22 flares outwardly adjacent to the pipeoutlet 25. More particularly, the area of the cross-sectional profiles27 in the last 10% of the length L of the tubular body 22 increases by20% or more. In FIG. 4, this is shown as the area of the cross-sectionalprofiles 27 going from about 50% of the final value to 100% of the finalvalue, over the last 10% of the length L of the tubular body 22. Thecross-sectional area of the diffuser pipe 20 thus increases rapidly inthe last section of the diffuser pipe 20, right before the pipe outlet25, thereby forming a diffuser pipe 20 which flares outwardly, like atrumpet, at the end portion thereof. The cross-sectional area of thediffuser pipe 20 does not increase after the pipe outlet 25, andachieves the final value at the pipe outlet 25. The diffuser pipe 20therefore ends or terminates at the pipe outlet 25.

Referring to FIG. 4, the area curve 30A for the tubular body 22 in FIG.3 shows that the area of the cross-sectional profile 27 at the pipeoutlet 25 is more than 20% greater than the area of the cross-sectionalprofile 27 at a point or plane where the last 10% of the length L of thetubular body 22 begins. Stated differently, an area of thecross-sectional profile at the pipe outlet is at least 20% greater thanan area of the cross-sectional profile at a point upstream from the pipeoutlet a distance corresponding to 10% of the length of the tubularbody. The area curve 30A for the tubular body 22 in FIG. 3 shows thatthe area of the cross-sectional profile 27 at the pipe outlet 25 is morethan 25% greater than the area of the cross-sectional profile 27 at thebeginning of the last 10% of the length L of the tubular body 22. InFIG. 4, this is shown as the area of the cross-sectional profiles 27 forthe area curve 30A going from about 50% of the final value to 100% ofthe final value, over the last 10% of the length L of the tubular body22. Thus, for the area curve 30A, the cross-sectional profiles 27increase in area by 50% or more over the last 10% of the length L. Forthe area curve 30A, the area of the cross-sectional profile 27 at thepipe outlet 25 is more than 50% greater than the area of thecross-sectional profile 27 immediately upstream of the last 10% of thelength L. Thus the area of the cross-sectional profiles 27 in the last10% of the length L of the area curve 30A increases by more than 25%, orby at least 25%.

For the area curve 30A, the cross-sectional profiles 27 increase in areaby at least 40% over the last 20% of the length L of the tubular body22. In FIG. 4, this is shown as the area of the cross-sectional profiles27 for the area curve 30A going from about 40% of the final value to100% of the final value, over the last 20% of the length L of thetubular body 22. More particularly, the area of the cross-sectionalprofile 27 at the pipe outlet 25 in the area curve 30A is about 60%greater than the area of the cross-sectional profile 27 at the last 20%of the length L. The diffuser pipe 20 having the area curve 30A therebyundergoes an area change of at least 60% in the last 20% of the length Lof the diffuser pipe 20. Indeed, and as shown in FIG. 4, thecross-sectional profiles 27 of the area curve 30A increase in area bymore than 50% over the last 20% of the length L.

For the area curve 30A, the cross-sectional profiles 27 increase in areaby at least 50% over the last 30% of the length L of the tubular body22. For the area curve 30A, the cross-sectional profiles 27 increase inarea by at least 50% over the last 25% of the length L of the tubularbody 22. In FIG. 4, this is shown as the area of the cross-sectionalprofiles 27 for the area curve 30A going from about 33% of the finalvalue to 100% of the final value, over the last 30% of the length L ofthe tubular body 22. The diffuser pipe 20 having the area curve 30Athereby undergoes an area change of at least 50% in the last 25% of thelength L of the diffuser pipe 20.

The area curve 30A shows that the diffuser pipe 20 may undergo increasesin the area of its cross-sectional profiles 27 of 50% or more in thelast 10% of the length L of the diffuser pipe 20, in the last 20% of thelength L of the diffuser pipe 20, and/or in the last 25% of the length Lof the diffuser pipe 20.

Referring to FIG. 4, another possible area curve 30B for the tubularbody 22 in FIG. 3 shows that the area of the cross-sectional profile 27at the pipe outlet 25 is 20% greater than the area of thecross-sectional profile 27 at the last 10% of the length L of thetubular body 22. Thus the area of the cross-sectional profiles 27 in thelast 10% of the length L of the area curve 30B increases by 20%. In FIG.4, this is shown as the area of the cross-sectional profiles 27 for thearea curve 30B going from about 80% of the final value to 100% of thefinal value, over the last 10% of the length L of the tubular body 22.Another possible area curve 30C for the tubular body 22 in FIG. 3 showsthat the area of the cross-sectional profile 27 at the pipe outlet 25 is33% greater than the area of the cross-sectional profile 27 at the last20% of the length L of the tubular body 22. In FIG. 4, this is shown asthe area of the cross-sectional profiles 27 for the area curve 30C goingfrom about 66% of the final value to 100% of the final value, over thelast 20% of the length L of the tubular body 22. The area curve 30Dshows that the area of the cross-sectional profile 27 at the pipe outlet25 is 33% greater than the area of the cross-sectional profile 27 at thelast 30% of the length L of the tubular body 22. In FIG. 4, this isshown as the area of the cross-sectional profiles 27 for the area curve30D going from about 66% of the final value to 100% of the final value,over the last 30% of the length L of the tubular body 22.

The increase in cross-sectional area of the diffuser pipe 20 over ashort distance of the diffuser pipe 20 may allow for rapid diffusion atthe exit of the diffuser pipe 20. This may lead to increased staticpressure prior to providing the fluid flow F downstream into a plenumand ultimately into the combustion chamber of the combustor 16. Sincediffusion occurs rapidly and over a short distance at the exit of thediffuser pipe 20, there may be lower pressure loss when compared to aconventional diffuser pipe where diffusion occurs over a more gradualincrease in cross-sectional area. Thus the distribution of thecross-sectional area toward the exit of the diffuser pipe 20 may resultin higher static pressure recovery and lower loss. The area curve 30Efor such a conventional diffuser pipe, where diffusion occurs over amore gradual increase in cross-sectional area, is shown in FIG. 4. Ascan be seen, the cross-sectional area in the area curve 30E increases ina substantially linear manner over the length of the conventionaldiffuser pipe.

Still referring to FIG. 4, an upstream area of the diffuser pipe 20 hasa more gradual increase in the area of the cross-sectional profiles 27.Referring to the area curves 30A, 30B, 30C, the cross-sectional profiles27 increase linearly in area over an upstream segment of the tubularbody 22 starting at 0% of the length L of the tubular body (i.e. at theinlet 23) and terminating at approximately 80% of the length L. Theslope of the area curves 30A, 30B, 30C is substantially constant overthe upstream segment. Thus, the tubular body 22 represented by the areacurves 30A, 30B, 30C increase gradually in cross-sectional area over theupstream segment. Stated differently, the increase in area of thediffuser pipe 20 represented by the area curves 30A, 30B, 30C is muchgreater near the exit of the diffuser pipe 20 than further upstreamwithin the diffuser pipe 20. Thus, diffusion occurs through a majorityof the pipe length, and more diffusion occurs near the exit of thediffuser pipe 20. The upstream segment of the diffuser pipe 20 may alsohave other shapes and profiles.

As seen in FIG. 4, all of the area curves 30A, 30B, 30C, 30D, includingthe area curve 30E for the conventional diffuser pipe, have the samevalue for the area of their respective cross-sectional profiles 27 atthe pipe outlet 25. In an embodiment, the radius of the diffuser pipe20, its length L along the pipe center axis 21, and its overall arearatio are the same as that of the conventional diffuser pipe. Theprimary difference is that the diffuser pipe 20 performs less diffusionthrough a majority of the pipe length and more diffuser near the exit,compared to the conventional diffuser pipe.

FIG. 5 shows possible lines of the fluid flow F through the diffuserpipe 20. As can be seen, the fluid flow F may remain clean and orientedparallel to the pipe center axis 21 through most of the diffuser pipe20. The fluid flow F may be cleaner throughout upstream sections of thediffuser pipe 20 because of less diffusion, and there may be a reductionin separated fluid flow F near the exit. The exit flare of the diffuserpipe 20 may help to lower the average exit Mach number, may help toincreases Cp (static pressure recovery), and/or may help to lower theomega (ω) loss.

FIG. 6 shows equivalent cone angle (ECA) plotted along the length L ofthe tubular body 22, where the length L is provided as a normalizedmeanline length. A larger ECA value is generally an indication of morediffusion and potentially more pressure loss. A lower ECA value ispreferable when the flow path of the diffuser pipe 20 is turning (i.e.in the bend portion). A higher ECA value after the turning can indicatethat flow is diffusing more efficiently. It can be seen that thediffuser pipe 20 has a lower ECA through most of the length L of thediffuser pipe 20 when compared to a conventional diffuser pipe, whichcontributes to lower diffusion and loss in the bend portion 28 of thediffuser pipe 20. Static pressure recovery (Cp), losses (ω) and the ECAare determined according to the following formulae:

$C_{p} = {{\frac{P_{s,{outlet}} - P_{s,{inlet}}}{P_{r,{inlet}} - P_{s,{inlet}}}\mspace{14mu} \omega} = {{\frac{P_{t,{inlet}} - P_{t,{outlet}}}{P_{t,{inlet}} - P_{s,{inlet}}}\mspace{14mu} {ECA}} = {2 \times {\tan^{- 1}( \frac{\sqrt{\frac{A_{2}}{\pi}}\sqrt{\frac{A_{1}}{\pi}}}{L} )}}}}$

Where Ps is the static pressure, Pt is the total pressure (Ps+pressurefrom kinetic energy), A1 is the cross-sectional area of diffuser pipe 20at the inlet 23, A2 is the cross-sectional area of diffuser pipe 20 atthe pipe outlet 25, and L is the meanline length of the diffuser pipe20.

Referring to FIGS. 3 and 4, there is also disclosed a method ofincreasing static pressure of fluid at the combustor 16. The methodincludes conveying the fluid through the diffuser pipe 20 to rapidlydiffuse the fluid through a last 10% of the length L, over which across-sectional area of the diffuser pipe 20 increases by at least 20%.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Still other modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims.

1. A compressor diffuser for a gas turbine engine, the compressordiffuser comprising: diffuser pipes having a tubular body defining apipe center axis extending therethrough, the tubular body including afirst portion extending in a generally radial direction from an inlet ofthe tubular body, a second portion extending in a generally axialdirection and terminating at a pipe outlet, and a bend portion fluidlylinking the first portion and the second portion, the tubular bodyhaving a length defined between the inlet and the pipe outlet, thetubular body having cross-sectional profiles defined in a plane normalto the pipe center axis, an area of the cross-sectional profile at thepipe outlet is at least 20% greater than an area of the cross-sectionalprofile at a point upstream from the pipe outlet a distancecorresponding to 10% of the length of the tubular body.
 2. Thecompressor diffuser of claim 1, wherein the area of the cross-sectionalprofile at the pipe outlet is at least 25% greater than the area of thecross-sectional profile at the last 10% of the length of the tubularbody.
 3. The compressor diffuser of claim 2, wherein the area of thecross-sectional profile at the pipe outlet is 50% greater than the areaof the cross-sectional profile at the last 10% of the length of thetubular body.
 4. The compressor diffuser of claim 1, wherein the area ofthe cross-sectional profile at the pipe outlet is at least 40% greaterthan the area of the cross-sectional profile at the last 20% of thelength of the tubular body.
 5. The compressor diffuser of claim 4,wherein the area of the cross-sectional profile at the pipe outlet is atleast 50% greater than the area of the cross-sectional profile at thelast 20% of the length of the tubular body.
 6. The compressor diffuserof claim 5, wherein the area of the cross-sectional profile at the pipeoutlet is 60% greater than the area of the cross-sectional profile atthe last 20% of the length of the tubular body.
 7. The compressordiffuser of claim 1, wherein the area of the cross-sectional profile atthe pipe outlet is at least 50% greater than the area of thecross-sectional profile at the last 30% of the length of the tubularbody.
 8. The compressor diffuser of claim 7, wherein the area of thecross-sectional profile at the pipe outlet is 66% greater than the areaof the cross-sectional profile at the last 30% of the length of thetubular body.
 9. The compressor diffuser of claim 1, wherein thecross-sectional profiles increase linearly in area over an upstreamsegment of the tubular body starting at 0% of the length of the tubularbody and terminating at 80% of the length of the tubular body.
 10. Adiffuser pipe comprising a tubular body defining a pipe center axisextending therethrough, the tubular body including a first portionextending in a generally radial direction from an inlet of the tubularbody, a second portion extending in a generally axial direction andterminating at a pipe outlet, and a bend portion fluidly linking thefirst portion and the second portion, the tubular body having a lengthdefined between the inlet and the pipe outlet, the tubular body havingcross-sectional profiles defined in a plane normal to the pipe centeraxis, an area of the cross-sectional profile at the pipe outlet is atleast 20% greater than the area of the cross-sectional profile at a last10% of the length of the tubular body.
 11. The diffuser pipe of claim10, wherein the area of the cross-sectional profile at the pipe outletis at least 25% greater than the area of the cross-sectional profile atthe last 10% of the length of the tubular body.
 12. The diffuser pipe ofclaim 11, wherein the area of the cross-sectional profile at the pipeoutlet is 50% greater than the area of the cross-sectional profile atthe last 10% of the length of the tubular body.
 13. The diffuser pipe ofclaim 11, wherein the area of the cross-sectional profile at the pipeoutlet is at least 40% greater than the area of the cross-sectionalprofile at the last 20% of the length of the tubular body.
 14. Thediffuser pipe of claim 13, wherein the area of the cross-sectionalprofile at the pipe outlet is at least 50% greater than the area of thecross-sectional profile at the last 20% of the length of the tubularbody.
 15. The diffuser pipe of claim 14, wherein the area of thecross-sectional profile at the pipe outlet is 60% greater than the areaof the cross-sectional profile at the last 20% of the length of thetubular body.
 16. The diffuser pipe of claim 10, wherein the area of thecross-sectional profile at the pipe outlet is at least 50% greater thanthe area of the cross-sectional profile at the last 30% of the length ofthe tubular body.
 17. The diffuser pipe of claim 16, wherein the area ofthe cross-sectional profile at the pipe outlet is 66% greater than thearea of the cross-sectional profile at the last 30% of the length of thetubular body.
 18. The diffuser pipe of claim 10, wherein thecross-sectional profiles increase linearly in area over an upstreamsegment of the tubular body starting at 0% of the length of the tubularbody and terminating at 80% of the length of the tubular body.
 19. Amethod of increasing a static pressure of fluid exiting a centrifugalcompressor of a gas turbine engine, the method including: conveying thefluid through a diffuser pipe to rapidly diffuse the fluid through alast 10% of a length of the diffuser pipe over which a cross-sectionalarea of the diffuser pipe increases by at least 20%.
 20. The method ofclaim 19, comprising gradually diffusing the fluid over a segment of thediffuser pipe upstream of a last 20% of the length, a cross-sectionalarea of the segment increasing linearly over its length.